In view of growing concerns to preserve the quality of the environment, it appears essential to fit liquid hydrocarbon dispensers with a sensor for detecting leaks, regardless of where they originate within the dispenser.
Several detection systems have been proposed for this purpose.
Firstly, it is possible to detect the vapours from liquid hydrocarbons inside the dispenser. This can be achieved either by means of biological, optical or combined sensors or by measuring the density of vapours contained in the dispenser. However, in view of the very marked variety of temperatures, humidity and quality of installation at service stations, this type of detection triggers numerous false alarms or, even worse, no alarm at all. Biological sensors, furthermore, have a tendency to become poisoned by additives. When it comes to liquid hydrocarbons of the gas oil type, these generate no or little vapour and it is difficult to detect their presence other than by the odours of the additives which they contain.
It would be conceivable to detect leaks by taking pressure measurements at different points in the pipework system for the hydrocarbons. However, to detect slight leaks, it is necessary to have a perfect knowledge and model of the distribution of pressure in the passages depending on the conditions under which the dispensers are installed on site and the sensors need to be extremely sensitive, in order of several mbars, and be capable of withstanding pressure surges of more than 15 bars, which require extremely expensive equipment. Moreover, the software must exhibit a high degree of intelligence to be able to process data from the sensors. Finally, sensors operating in hazardous areas also need to be security-protected and are therefore very expensive.